Subversion Repositories open8_urisc

--                           and stack pointer as well.

--                           and stack pointer as well.

-- Seth Henry      05/24/20 Removed the Default_Int_Flag, as it is covered by

-- Seth Henry      05/24/20 Removed the Default_Int_Flag, as it is covered by

--                           Supervisor_Mode. If Supervisor_Mode isn't set,

--                           Supervisor_Mode. If Supervisor_Mode isn't set,

--                           code can simply use STP to set the bit

--                           code can simply use STP to set the bit

-- Seth Henry      06/09/20 Added ability to use unsigned index offsets for

-- Seth Henry      06/09/20 Added ability to use unsigned index offsets for

--                           for indexed instructions, reducing the final

--                           for indexed instructions, reducing the final

--                           address generator to a multiplexor fed only by

--                           address generator to a multiplexor fed only by

--                           registers.

--                           registers.

library ieee;

library ieee;

  -- The original model treated the offset to LDO/STO as a signed value

  -- The original model treated the offset to LDO/STO as a signed value

  --  allowing access to locations -128 to +127 from [Rn+1:Rn]. This isn't

  --  allowing access to locations -128 to +127 from [Rn+1:Rn]. This isn't

  --  always helpful, so the generic allows the CPU to use unsigned math

  --  always helpful, so the generic allows the CPU to use unsigned math

  --  for the offsets. This makes the range 0 to +255 instead.

  --  for the offsets. This makes the range 0 to +255 instead.

Unsigned_Idx_Offsets : if( Unsigned_Index_Offsets )generate

Unsigned_Idx_Offsets : if( Unsigned_Index_Offsets )generate

  IDX_Offset(15 downto 8)    <= (others => '0');

  IDX_Offset(15 downto 8)    <= (others => '0');

  IDX_Offset(7 downto 0)     <= Operand1;

  IDX_Offset(7 downto 0)     <= Operand1;

end generate;

end generate;